Synthetic diamonds were first made by General Electric Company in the US in 1955. In their process, carbonaceous compounds are subjected to pressures of 400 tons per square inch at temperatures of 5000 degrees F. The diamonds thus produced are suitable for industrial uses only.

In the late 1960's a method was developed for "growing" diamonds by heating a diamond particle to a high temperature and subjecting it to methane gas. The gas decomposes into carbon atoms which adhere to the diamond crystal. The crystal structure of the enlarged diamond is identical to that of a natural diamond. Diamonds of gem size had not been produced by the 1970's using this method.